Here is the full list of all 34 Demonheart achievements.
Finish Chapter 5.
Kiss Ari.
Decipher the whole message in Chapter 5.
Finish Chapter 4.
Read all the entries of Rivera's journal.
Decipher the message in Chapter 4.
Finish Chapter 3.
Ask the demonspawn as many questions as you can.
Decipher all the messages in Chapter 3.
Max out both Good and Tactful points.
Finish Chapter 2.
Decipher the message in Chapter 2.
Finish Chapter 1.
Decipher all the messages in Chapter 1.
Max out both Evil and Tactful points.
Max out both Good and Defiant points.
Max out both Evil and Defiant points.
Read the book about demonspawn in Chapter 1.
Examine Mr. Edgardo after the dinner with Orchid.
Molest the demonspawn.
Kill Mark.
Kiss Sir Brash.
Finish the game as Good Bright and as Evil Bright.